[GRASS-user] Level LiDAR data to gps points

[Vaclav Petras]

On Tue, Dec 19, 2017 at 3:29 AM, Shane Carey <careyshan at gmail.com> wrote:

>
> I have some LiDAR data that was not levelled properly and I was wondering
> does anybody know of a way of levelling the las files to gps points?
>
>
Hi,

if the issue is really just vertical (which is usually the case), you can
use v.transform zshift to shift by the given value. For rasters, e.g. DEM
based on binning the lidar points with r.in.lidar, you can use r.mapcalc to
shift it (e.g. expression "new = old + 2").

The shift can be determined by binning (or even interpolating) the points,
followed by querying raster using the GPS points as a vector using
v.what.rast, and then by computing the difference using v.db.addcolumn and
v.db.update. Finally, you can average the difference using v.db.univar. One
(average) values will be usually good enough for lidar point cloud, for UAV
point cloud, spatially variable shift might be needed.

Vaclav
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